Textbook of Maritime Medicine

Introduction

In this chapter the relevance and different forms of cardiovascular diseases in seafaring are discussed, including diagnosis and treatment. The special features of laymen medical care at sea - often far away from professional medical aid - are taken into account. During the last century, cardiovascular disease (CVD) has developed to a leading cause of morbidity and mortality worldwide. By 2020 it is projected that CVD will have surpassed infectious disease as the worlds leading cause of death and disability (1).

10.1.1 Epidemiology of CVD

Ehara et al. (2) analysed the Japanese disease statistics for seamen over fifteen years (from 1986 to 2000) and found that CVD (11.6%) were the third most frequent diseases aboard. It has been repeatedly described that seafaring belongs to the high risk occupations of ischemic heart diseases (3,4,). Jaremin and Kotulak (5) performed a retrospective study from 1985 to 1994 based on a population of 11,325 Polish seafarers and deep-sea fishermen. They found more than 70% of the documented mortalities at sea were caused by myocardial infarction. Also other mortality studies confirmed CVD as an important cause of seafarer’s deaths (mortality rate between 30 and 45 per 100.000 seafarer-years) (6,7,8).

In recent years, due to rising economic pressure and shipboard organizational changes with elevated individual responsibility an increase of physical and psychical stress and consequently a higher risk of CVD among seamen have been assumed. Compatible with this assumption, CVD are becoming increasingly important for naval disablement among seamen. At the beginning of the 90s the naval disablement in Germany was related in 13% to 14% to CVD, whereas the current proportion is higher than 18% (9).

10.1.2 CVD risk in different seafarers’ groups

In a German cross-sectional study 161 seafarers operating on German-flagged vessels were examined. This study showed that Europeans compared with non-Europeans were about twice as likely to have more than 3 cardiac risk factors after adjusting for age (OR 2.4 (95% CI 1.01 - 4.55) (10); especially engine room officers (43.3%) and the galley/ operating staff (57.1%) showed a higher CVD risk judged by the number of risk factors (in contrast to 33.3% of deck officers, 24.4% of crew ranks on deck, 20.0% of crew ranks in the engine room).

Individual CVD risk factors

Besides genetic and ethnical determinants, CVD risk is generally influenced by independent coronary risk factors, namely age, LDL cholesterol, smoking, HDL cholesterol, systolic blood pressure, family history of a premature myocardial infarction, diabetes, and triglycerides, as well as dependent risk factors, i. e. overweight, lack of exercise, high-fat diet and alcohol (11).

Some of these risk factors are modifiable and related to the specific conditions aboard so that a high frequency of independent CVD risk factors respective contributing factors in seafarers has been repeatedly described (12). For example, the crew has scarcely an influence on the usually unbalanced and high-fat diet aboard (13) contributing to high cholesterol, high triglicerides and obesity. Hyperlipidemia is often observed in crews, e.g. among 40% of investigated Chinese seafarers (14); high cholesterol was measured in 80% and high glucose in 30% of Croatian seamen (15). Among Lithuanian mariners 44.9% showed age-standardized a clinically significant elevation of blood pressure (compared to 53% of the general population of Lithuania (4); the leading risk factors encompassed increased body mass index (66.5% had a BMI higher than 25 kg/m²), smoking (55.2% smokers) and alcohol use

(82.5%). Among seafarers of German-flagged vessels the most prominent CVD risk factors in seafarers were shown to be hypertension (49.7%), high triglycerides (41.6%), older age (39.8%), and smoking (37.3%) (10). The seafarer’s cigarette consumption as an important CVD risk factor is higher than in the general population (10,4,16).

Besides the mentioned parameters, also psychosocial work factors such as stress pose a contributing CVD risk factor. Kivimäki et al. (17) observed in their broad meta-analysis of prospective cohort studies that stress at work increased the CVD risk by 50% on average. It is described that seafaring constitutes a high psychophysical stress for crews (18). Not only emergency events but also the shipboard routine often result in a high level of stress. Restricted leisure time facilities on board often lead to a lack of exercise and consequently to overweight. Owing to the unique unity of workplace and limited leisure area on board - frequently lasting for months - seafarers are exposed to stress to an exceptional degree and consequently to a higher CVD risk (19).

Considering the presence of multiple CVD risk factors in seamen specific occupational preventive measures (such as smoking cessation, weight control and use of anti-stress techniques) should be performed, especially in older seafarers. They should be extensively informed about their lifestyle related CVD risk and motivated to omit unhealthy behavior. Presence of cardiovascular risk factors contributes to an increased risk of ischemic heart disease as well as cerebrovascular illnesses.

CVD risk assessment in seafarers

Nowadays, several population-based risk scores exist to assess the individuals’ CVD risk, e.g. for a 10-year period. On account of the usually multinational crews and consequently the obviously different basic risk, a coronary risk assessment by applying only one population-specific risk score is not possible. Thus, to assess the seafarers’ 10-year CVD risk, a stratification of their country of origin is mandatory.

German seafarers compared with the German population of the PROCAM study working ashore showed a similar predicted 10-year CVD risk; taking into account the healthy-worker-effect due to the periodical test for nautical fitness a higher coronary risk of the seafarers can be assumed (10). The application of such CVD-risk scores can be easily implemented in the fitness examinations for nautical service and would probably help to reduce the frequency of dangerous CVD incidents at sea (12).

10.1.3  Heart diseases

Cardio-vascular diseases comprise heart diseases (e.g. coronary heart disease, cardiac insufficiency, cardiac arrhythmia) and circulatory disorders (e.g. arterial hypertension/ hypotension, stroke, acute obliteration in the limbs, pulmonary embolism, venous disorders). Severe chronic cardiac problems such as chronic heart failure are relatively seldom. This is obviously due to pre-employment examination and repeated medical fitness tests in the merchant marine service. Most of the life-threatening cardiac events on board are caused by acute ischemic cardiovascular diseases (CVD). Among CVD, the coronary heart disease plays a predominant role

Coronary heart disease

Hammar et al. (20) found in nautical officers a 1.9 times increased risk of myocardial infarction. According to Ehara et al. (2), among Japanese officers in particular captains showed a high prevalence of CVD (16.3%). Out of the above mentioned 11,325 Polish seamen (1985 – 1994), 109 ones had a myocardial infarction at sea; they consisted of 20 nautical officers or captains, 18 engine room officers, 33 able bodied seamen, 26 crew ranks of the engine room and 9 galley staff members (5).

Increasing age leads to a lack of blood vessel’s elasticity and to a calcium deposit that can accumulate on their inner walls. Also coronary blood vessels are affected by this process and become narrower. In case of acute pain of the chest (angina pectoris) as an early stage of myocardial infarction the coronary arteries are narrowed but not altogether blocked. In acute overexertion the heart workload increases and the heart muscle becomes short of blood resulting in typical angina pectoris symptoms.

If a blood clot completely blocks a coronary artery the respective blood and oxygen supplying area of the heart muscle dies as a sign of myocardial infarction.

CHD poses the commonest heart disease in people over 50 years of age but can also happen in younger people especially in coincidence with metabolic disorders.

CVD symptoms

Acute CVD symptoms are characterized by dull and oppressive pains predominantly in the left half of the chest often radiating out in the shoulders, the left arm or in the neck and lower jaw. Atypical symptoms may occur and be highly variable e. g. sweating or weakness and anxiety. CVD symptoms may be elicited by strong physical activity.

CVD diagnosis

In case of severe chest pain of a seaman the officer responsible for shipboard medical care (“health officer”) has to immediately check the patient’s pulse rate and heart rhythm. The differential diagnosis of chest pain must include ruptured aorta, embolism, pneumonia, pleurisy, pneumothorax or shingles. The medical assistant service should be directly contacted for further consulting, location of pain should be asked, physical examination be done, information about preexisting symptoms or cardiac incidents, age, smoking habits, presence of diabetes mellitus, history of heart disease in the family be gathered and possibly an early evacuation be intended.

Nowadays, it is possible to diagnose damage to the heart muscle by on the spot quick-tests (Tropinin-test) suitable also for the use by trained, non-medical persons like seamen. Further, the seaman’s ECG which can be transmitted to the telemedical assistant service provides worthwhile information about the cardiac rhythm of a patient with unspecific thoracic complains. Since the benefit of treatment for myocardial infarction is reduced after only a few hours delay quick diagnosis of CVD maybe life-saving. Thus, some flag-states have already implemented the Tropinin-test and/ or an ECG device (as a part of a semiautomatic defibrillator) in their statutory medical chest. The Tropinin-test and the ECG are of particular importance in the decision to administer anti-thrombotic substances such as acetylsalicic acid respective medicines for heart arrhythmia (Verapamil).

CVD treatment

First of all, the seaman with chest pain is advised to stay in bed except to go to the toilet. According to medical advice acetylsalicic acid, nitrolingual spray, metropolol, diazepam and a strong pain-killer (preferably morphine) should be administered if available on board. Further, oxygen should be given through a mask. The patient’s current clinical status should be continuously observed by a crew member until professional aid arrived on the vessel. If the patient is conscious “the heart position” (sitting half-upright, back supported by a pillow, legs hanging) should be taken. The continuous monitoring of an ECG and its transmission ashore to the medical assistance centre is very helpful.

Acute unconsciousness often indicates a life-threatening arrhythmia, a severe cardiac failure or even a cardiac arrest. In such cases only the immediate cardio-pulmonary resuscitation, ideally in association with a semiautomatic defibrillator, is life-saving.

On board of merchant ships usually a health officer as a medical layman holds the responsibility for medical care. Thus, the diagnoses and treatment at sea mainly depends on his experience. His first-aid measures rely on his medical training which often took place several years ago. This training should qualify the seaman to check and to control basic cardiac parameters such as heart frequency and blood pressure as well as to cope with the resuscitation technique according to updated, currently valid first-aid recommendations.

CVD prognosis

The prognosis of a coronary event at sea is different from that ashore. This is mainly due to limited primary medical care aboard. For example, the mortality rate of myocardial infarction among Polish seafarers was similar to that of the general Polish population in spite of the expected healthy-worker effect of seamen (only 24.5% of subjects with a myocardial infarction at sea survived one year) (5); it is assumed that the survival after a myocardial infarction at sea might be less favorable than that ashore due to a lack of early intervention as angioplasty or lysis. Further reasons for the worse prognosis after a myocardial infarction at sea might be that the team of rescuers on board is often inexperienced, the rescue/resuscitation action is frequently delayed, and the evacuation ashore is often difficult or impossible.

The CHD prognosis mainly depends on the fast and correct diagnosis. In case of unspecific thoracic symptoms, the causes should be identified first. Due to the often unclear genesis of symptoms (cardiac, pulmonary or orthopedic), a competent medical evaluation is necessary. Since seamen are in general not capable of doing this, they need (telemedical) advice by a physician ashore.

Cardiac failure

Cardiac failure can occur as a consequence of survived heart attack, of longstanding untreated hypertension, of congenital valvular defect, of (viral) myocarditis or of alcoholic disease.

The patients suffer from dyspnoea after slight effort, raised and often irregular pulse, lack of physical capacity, blue lips, swollen feet and lower legs. They should be advised to have physical rest in an upright sitting posture. According to medical advice oxygen, nitro drugs or drugs for water excretion may be administered before hospital treatment.

Cardiac arrhythmia

Febrile infections with a life-threatening inflammation of the heart muscle, heart infarction, congenital factors or severe hypothermia can lead to dangerous arrhythmia. The latter can result in a fall of blood pressure, faintness and some patients may suffer from shortness of breath. Many patients develop palpitations and the feeling that their heart has stopped. Sometimes these symptoms are accompanied by chest tightness, dizziness, unconsciousness or light-headedness

Cardiac arrhythmia treatment

The patient’s pulse as well as blood pressure should be permanently controlled. (For the seamen it might be demanding to judge the cardiac rhythm especially at high heart frequency. Feeling the pulse and measuring blood pressure are important findings for making a diagnosis and this needs to be trained.)

If the cardiac palpitations persist the patient should rest in bed with slightly raised upper body and legs low until the symptoms disappear. Medical advice should be sought with a view to evacuation, especially in case of a rapid or irregular pulse rhythm or if symptoms like chest tightness, pain in the chest or episodes of unconsciousness occur during palpitations.

In case of potentially arrhythmic heart diseases a definitive medical advice is scarcely possible without knowing the patient’s ECG. Drugs for cardiac arrhythmias used wrongly can intensify or even elicit abnormal heart rhythm. Thus, it may be dangerous to administer drugs without noticing the patient’s cardiac rhythm. According to the International Medical Guide of Ships (3^rd edition) the rescuer should give metoprolol to patients with palpitation if medical advice cannot be obtained.

In suspected cardiac arrhythmia a telemedical transmitted ECG is of great value -provided that the vessel is equipped by additional medicines for heart rhythm disturbance (verapamil, atropine). At present, the discharge and transmission of an ECG can be realized via semi-automatic defibrillators operated by laymen. In addition to shock treatment during ventricular fibrillation (accounting for 80% of sudden cardiac deaths), defibrillators can take on the medically helpful function of telemedicine at sea. By means of the transmitted ECG it is possible for the physician ashore to diagnose cardiac arrhythmic disorders and to advise anti-arrhythmic drugs available on board. It should be mentioned that the relevance and the cost-benefit ratio of semi-automatic defibrillators are controversially discussed among practitioners in maritime medicine.

10.1.4  Circulatory disorders

Circulatory disorders comprise e.g. blood pressure abnormalities and blocked arteries or veins of different organs.

Arterial hypertension

Risk factors for arterial hypertension are higher age, renal damage, smoking, stress as well as some drugs (“pill”). Arteriosclerosis may also elicit high blood pressure. Patients with arterial hypertension often suffer from dyspnoea after slight effort, high and often irregular pulse, lack of physical capacity, blue lips, swollen feet, headache, nausea and dizziness.

Patients with hypertensive crisis should stay in bed and the blood pressure has to be repeatedly monitored. According to medical instructions nitrolingual spray should be given. In the next port the seaman needs to be referred to a medical doctor to determine the cause of hypertension and to optimize treatment.

Predominantly young, slim people sometimes have a low blood pressure. Many of these patients have blackouts if they stand for a longer time or stand up quickly from a lying position.

After lying the patients flat they will recover rapidly. A further treatment including long-lasting rest is normally not necessary. Physical training on board may help to raise the pulse rate as a long-term effect. Differential diagnostics should be done if symptoms repeatedly occur.

Stroke

Pathogenetically, a stroke is caused by a complete occlusion of an artery supplying blood to the brain (ischemic stroke). It is triggered by a plaque or clot (thrombus) in 65-75% of strokes or by a clot formed in a vessel elsewhere in the body and swept by the bloodstream until it occludes a blood vessel in the brain (5-10% of strokes). The bleeding into the brain (hemorrhagic stroke) from a ruptured artery supplying blood to the brain occurs in 20% of strokes.

Stroke symptoms

Stroke patients develop symptoms gradually over hours or days. They often get complete or partial paralysis of one side predominantly affecting face and arm. A weakness of the face is shown by dropping of one corner of the mouth. Further, they have headache and an abnormal speech with difficulties to find words.

Stroke diagnosis

In case of suspected stroke the patient has to be carefully examined to find out any weakness or other stroke symptoms. (Thus, the inexperienced examiner on board should be aware about the typical symptoms and must be able to judge the patient’s power in the bilateral extremities’ comparison. This might be demanding for several health officers).

Before seeking for medical advice the pulse rate, blood pressure, level of consciousness and some history data (about age, taken medicines, known diabetes/ epilepsy or evidence of cocaine or amphetamine use) have to be noted. An urgent hospital admission is essential, even if there has only been slight and transient paralysis because first the cause of the stroke should be professionally clarified and second these patients are at risk to develop a massive stroke in the course of time.

Stroke treatment

The patient should lie in bed with the body, shoulders and head at the same level for at least the first 24 hours. In case of unconsciousness the patient should put in stable lateral position; it must be avoided to give anything by mouth until it is ensured that the patient can swallow water normally. In unconsciousness an intravenous cannula has to be inserted and normal saline administered. According to the International Medical Guide for Ships (3^rd edition) it is recommended to give docusate with senna and acetylsalicylic acid if shipboard evacuation is likely to be delayed for more than 24 hours.

Acute arterial obliteration in the limbs

Arteries of the limbs can be obliterated by a clot coming from the heart or from another diseased artery (by arterial embolism or arterial thrombosis). Common risk factors are cardiac arrhythmia, aortic aneurysm, smoking and an age above 50 years.

The patients normally have a long history of sudden, exertion-related pain in the muscles of the affected limbs becoming pale, cold and without a pulse. In most cases the arteries of the legs are affected leading to pain in the calf muscles during walking in terms of the so-called intermittent claudication. Sometimes, in severe cases, shock with a rise in pulse or fall of blood pressure as well as fever appears. On rest the symptoms normally disappear.

The affected limbs must be in a low position in warming clothing. The patient has to stay in bed and the pain must be killed by strong drugs (preferably morphine). The immediate evacuation and hospitalization are required because the affected limbs could otherwise die off and then have to be amputated. The health officer should be able to distinguish embolism from thrombosis because of therapeutic consequences.

Pulmonary embolism

When thrombi from major veins swept on with the bloodstream to the blood vessels of the lung they may occlude a lung artery. This is often caused by deep vein thrombosis. Massive pulmonary embolism may elicit a serious state of shock and is often fatal. These patients suffer from sudden weakness, breathlessness, anxiety and pain in the chest.

First at all, the patient’s shock needs to be treated. The patient sits with raised upper body by strictest bed rest. As pulmonary embolism poses a serious life-threatening event immediate hospital treatment is required.

Venous thrombosis

A venous thrombosis initially starts with an inflammation of the vain wall (phlebitis), predominantly in varicose vein of the lower legs. Venous thrombosis occurs especially in patients who had a surgery during the previous four weeks or who have been immobile for more than 10 hours (probably a seaman arriving the ship after a long plane flight).

The affected limbs become red, hot and pressure-sensitive. Further, the limbs are swollen and lifting the foot becomes painful. Some days later the symptoms abate and the vain scleroses.

The patient should rest for at least 10 days in bed since a risk of embolism exist. The limbs should be raised (in contrast to the treatment of embolism), cooled and alcohol compresses should be administered. Further, anti-inflammatory drugs should be given. After inflammation has abated elastic bandage to limbs should be applied and the patient is permitted to walk.

Conclusion

Seafarers have a lot of job-related risk factors for CVD. Taking into consideration the healthy-worker effect due to the pre-employment examination and the periodical medical fitness tests seafarers seem to be at (slightly) elevated risk for cardio-vascular diseases compared to the reference population ashore. The prognosis of acute severe CVD often depends on the measures taken in the first few hours after occurrence of the symptoms. Diagnosis and treatment of CVD are a considerable challenge for the medical lay-person on board and necessitate a close interaction with the medical assistant service. As the medical advice usually relies on the information given by non-medical health officers these persons have to be well-trained. Thus, medical refresher courses at a high standard should train the first-aid skills and can consequently improve the outcome, in severe cases the survival, of patients with CVD at sea. It can be assumed that additional diagnostic parameters such as Tropinin-quick test or ECG (recorded by a semi-automatic defibrillator and interpreted by a radio medical centre) will further improve efficiency of treatment of patients with acute cardiovascular diseases.

As prognosis of CVD is worse at sea compared to that on-shore the question about the medical fitness-decision raised especially in seamen who obviously have increased CVD risks or already have suffered from heart diseases. This topic is discussed elsewhere in the textbook. More effort should be paid to raise the seafarer’s awareness about their individual risk for CVD and to advice them on prevention. It should be a joint attempt of the shipping company (e.g. by a satisfactory offer of shipboard exercise possibilities, a more balanced diet or of health information campaigns), the ship masters (e.g. by active motivation of his crew to use these offers) and the seafarers themselves (e.g. to abandon poor health and eating habits and to be more responsible for their health promotion).

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